Better Roads

August 2014

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Better Roads August 2014 17
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elaborate steel framework is possible,
which can reduce girder size and result
in a stronger, more durable product.
SCC mixes also contain less entrained
air, so fewer bubbles and "bug holes"
appear in the finished product to cre-
ate a smoother, more aesthetically
pleasing surface.
The flowability of SCC is measured
in terms of spread when using a modi-
fied version of the slump test (ASTM C
143). The spread (slump flow) of SCC
typically ranges from 18 to 32 inches
depending on the requirements.
Most SCC mixes require an increase
in the proportion of fines and a reduc-
tion of coarse aggregate compared to
traditional concrete. This raises con-
cerns that the materials' shear resistance
may be adversely affected, and that
stiffness may be compromised. Re-
searchers hope that the results of testing
on this bridge will prove the materials'
merit and clear the way for the use of
SCC on future transportation projects.
The three-span Highway 50 bridge
contains three sets of girders fabricated
by County Materials' Bonne Terre, Mo.,
plant. The girders for the first span are
made from a standard SCC mix. The
second set of girders is manufactured
with a high-strength SCC. This mix
contains a higher percentage of cement
for a stronger, more durable product
with a compressive strength of up to
14 KSI. The third span is constructed
with a standard Missouri DOT ap-
proved concrete mix design and func-
tions as the control in the experiment.
Sensors embedded in the girders
and bridge deck will allow researchers
to monitor the materials' performance
over time, and provide real-world data
about their relative strength as well as
detailed information on the bridge's
internal stresses.
He says using the high-strength self-
consolidating mix allowed the span
length to increase by 20 percent, and
is expected to reduce maintenance
costs over the life of the structure.
"Most of the current bridges (in Mis-
souri) have a service life of 25-50
years," Myers says. "We're hoping to
double that."
For more information on this project, go to
countymaterials.com/projects/bridge-girders-
a-prestress/item/s-t-bridge-project-in-
missouri?category_id=201.